1. Field of the Invention
This invention relates to the field of human dietary supplements, and more specifically to improved supplements comprising organochromium complexes derived from yeast.
2. Background
The physiological assimilation of an adequate quantity of heavy metals is essential to human health. Failure to ingest and absorb the necessary amounts of such metals can lead to improper functioning of the body's metabolic processes, and to various diseases and disorders. In particular, chromium deficiency can be a major problem in the human diet. Inadequate intake of chromium has been linked to an increased risk of heart disease, diabetes, hypoglycemia, obesity, impaired metabolism, and diminished longevity. Heart disease and diabetes alone account for about sixty percent of all deaths in the United States each year, and death usually strikes these victims ten to twenty years before they reach the average life span. The National Academy of Sciences has recommended an intake for humans of about 50 to 200 micrograms of trivalent chromium daily. It has been reported that about 9 out of 10 adults fail to ingest even the minimum recommended amount.
Trivalent chromium (Cr.sup.3+) describes the charged state of chromium species present in foods and, thus, supplementation with Cr.sup.3+ is useful in dietary supplements. Other forms of chromium, such as Cr.sup.4+ and Cr.sup.6+, are quite toxic and are not useful in supplementing the human diet. Trivalent chromium may be complexed to organic or inorganic ligands, forming organic and inorganic forms of trivalent chromium respectively. Both organic and inorganic forms of chromium have been used as dietary supplements.
Biological activity of chromium is highly dependent upon the type of coordinate complex formed with the chromium. A chromium coordinate complex is formed when an organic ligand is bound to trivalent chromium in a configuration that involves both covalent/ionic and non-covalent forces to stabilize the complex. The biological activity of a complex depends upon its bioavailability. Inorganic chromium compounds have been shown to have much less bioavailability than organic coordination compounds. [M. M. Wang et al., Nutr. Res., 9:989-998 (1989)]. A possible explanation is that since organic chromium complexes have greater membrane solubility than their inorganic counterparts, organic complexes have better bioavailability and, hence, have higher biological activity.
One of the major nutritional roles of trivalent chromium appears to be its effect in glucose metabolism. Specifically, a deficiency in chromium in the diet has been linked to impaired glucose tolerance, i.e., reduced ability to maintain blood glucose at normal levels. The transport of glucose and vital amino acids into the cell for energy and protein synthesis is facilitated by the binding of insulin, which is an important hormone for the human system since it is involved in the control of muscle growth, body weight, cardiovascular health and many other vital metabolic functions. Mertz has shown that an organic trivalent chromium complex called Glucose Tolerance Factor ("GTF") is responsible for binding insulin to cell membrane insulin receptor sites. [Mertz, W., "Chromium Occurrence and Function in Biological Systems," Physiol. Rev., 49:163-239 (1969), "Mertz I"]. The exact structure of active yeast-produced GTF is not well defined. However, chemical analysis of GTF shows that GTF is comprised chiefly of trivalent chromium and niacin, and contains glycine, glutamic acid, and cysteine. [Evans, G. W., et al., Biochem. Biophys. Res. Comm., 50:718-722 (1973)]. Hence, chromium having GTF chromium activity is essential to the maintenance of blood glucose levels.
3. Description of Prior Art
Since the human diet is frequently deficient in chromium content, dietary supplementation with highly bioavailable, non- toxic chromium agents is desirable. A major shortcoming of using Brewer's yeast as a source of naturally occurring GTF as supplemental dietary chromium is that the active form of chromium ion is formed in very low concentrations in Brewer's yeast. As a result, the average human would have to consume at least ten tablespoons of Brewer's yeast per day in order to get about 40 micrograms of biologically active chromium. Attempts at extracting or concentrating GTF from Brewer's yeast have been reported as reasonably successful, but the expense of the processing required for producing a commercial food supplement by these methods is prohibitive for the development of a viable commercial product. [Toepfer, E. et al., J. Agr. Food Chem., 21(1): 69-73 (1973) "Toepfer I"]. Thus, inorganic and organic complexes of trivalent chromium have been developed with hopes of providing safe alternative sources of supplemental chromium having similar biological activity to GTF derived from Brewer's yeast.
The prior art provides for dietary chromium which can be used to supplement the diet from two distinct sources: chemical synthesis (of inorganic and organic forms of chromium) or biological processing by yeast (chromium-enriched yeast). Although synthetic inorganic chromium compounds, such as chromium chloride, chromium oxide, and chromium acetate, have been shown to have very low bioavailability, they do show limited activity as dietary supplements. [Anderson, R. and Kozlovsky, A., Am. J. Clin. Nut., 41:1177-1183 (1985); Liu, V. J. K., et al., Am. J. Clinical Nutrition, 31:972-976 (1978)]. Unfortunately, these inorganic chromium compounds have also been shown to have appreciable toxicity to the human system. [Mertz, W., Newer Trace Elements in Nutrition, 7:123-159 (1971) "Mertz II"].
Trivalent chromium complexed with various organic ligands has been used to adequately supply chromium to the human body. Experiments have shown that some of these chromium complexes are better absorbed and utilized by the body than elemental or inorganic salt forms of chromium. [See, e.g., Evans, U.S. Pat. No. 4,315,927]. However, a major shortcoming of the compounds in which trivalent chromium is complexed with organic ligands, specifically, picolinic acid, is their inherent water insolubility. Such insolubility may hinder the efficacy or absorption of chromium by intestinal membranes, ultimately leading to only a fraction of the chromium being available to effect its nutritionally beneficial actions. Another drawback of using chromium picolinates as dietary supplements is the potential for chromosomal damage when the complexes are introduced into cells. [Brody, J., "Chromosome Damage in the Lab is Tied to a Chromium Supplement," New York Times, Oct. 25, 1995]. Nicotinate salts of trivalent chromium have also been used for supplementation to the human diet. These chromium nicotinate compounds have demonstrated biological action in some experiments, however, they show decreased activity in some key metabolic assays where the efficiency of chromium metal uptake by the human intestine was investigated. [See, Evans, cited above].
Attempts to obtain compounds with appreciable GTF biological activity have also been made. [Toepfer, et al., J. Ag. Food Chem., 25(l):162-166 (1977) "Toepfer II"]. Toepfer teaches the reaction of nicotinic acid and amino acids with chromium chloride in refluxing alcohol. However, the biological activity of these compounds are marginal, the reflux reaction generates limited yields, and the products are hard to characterize and are of limited stability. A method for synthesizing a trivalent organochromium species comprised of contacting an alkali metal salt of nicotinic acid with a trivalent chromium salt is known. [Jensen, U.S. Pat. No. 4,923,855]. The resulting chromium complex is a form of chromium that is purportedly a useful supplement to the human diet since it has been demonstrated to have GTF activity comparable to Brewer's yeast. However, this complex has poor solubility.
Chromium complexed with various amino acids has also been reported. Certain chelated compounds can be used as feed supplements for animals. [See, e.g., Ashmead, U.S. Pat. No. 4,020,158]. Specific buffer systems have been used to derive ligands for trivalent chromium from hydrolyzed protein concentrates in the production of feed supplements for animals. [See, Jenson, U.S. Pat. No. 4,187,364]. Trivalent chromium complexed with a vitamin ligand, e.g., nicotinic acid and, optionally, an .alpha.-amino acid have been prepared. [Ashmead, U.S. Pat. No. 5,292,729]. Such compounds have appreciable biological activity similar to Brewer's yeast.
Most notably, Brewer's (or Baker's) yeast also contains active forms of trivalent chromium. The terms Brewer's and Baker's yeast are known in the art to refer to the same strain of yeast. It has been shown that Glucose Tolerance Factor (GTF) from Brewer's yeast is an effective form of chromium that is essential for human metabolism. [See, Mertz Archives of Biochem. and Biophvs., 85:292-295 (1959), "Mertz III"]. GTF can be produced by niacin or tryptophan, glycine, glutamic acid and cysteine, as well as a source of chromium, usually inorganic chromium. The trivalent chromium complexes naturally produced in low yields in Brewer's yeast are known to be highly active. Indeed, the most active source of naturally occurring chromium is found in Brewer's yeast. [Mertz, W., Present Knowledge in Nutrition, 36:365-372 (1976), "Mertz IV"].
Other forms of chromium yeast have been reported. For example, chromium derived from Brewer's yeast has reported chromium concentrations of about ten to thousand-fold greater than those of Mertz IV (cited above) has been produced. [See, Skorgerson, U.S. Pat. No. 4,348,483]. A method of concentrating organic chromium complex in Brewer's yeast comprising a nutritional media of chromium oxide, and specific quantities of certain amino acids has been reported. [See, Szalay, U.S. Pat. No. 4,343,905]. These sources of biologically active chromium are obtained by the processing of yeast having an enriched chromium content. It is believed that these processed "chromium yeast" have a much greater concentration of chromium than is naturally occurring in Brewer's yeast, which is typically about 5 ppm. [Offenbacher, E., Am. J. Clinical Nut., 42:454-461 (1985)]. As reported, these chromium-yeast metabolically process the chromium, thereby producing chromium coordination complexes with high GTF activity.
Inorganic forms of chromium have been used as feed for yeast in order to produce these chromium coordination complexes of high GTF activity. For example, a method for producing chromium-enriched yeast (Brewer's yeast, Torula yeast, or S. uvarum) that employs an aqueous solution of inorganic chromium salts such as CrCl.sub.3 with growth media, and with a pregrowth incubation period to cultivate the yeast is known. [Skogerson, U.S. Pat. No. 4,348,483]. Chromium content of the yeast produced using this process is from about 500 ppm to about 1,000 ppm. However, this process entails internalization of the inorganic chromium salt without complete metabolization, resulting in a high probability that a significant amount, if not all, of the chromium found in the chromium-enriched yeast is inorganic chromium. Hence, the chromium produced in this process is not GTF active chromium yeast, but is rather inorganic trivalent chromium salts mixed with the structural material of yeast. As such, the chromium produced using this method does not possess high bioactivity and is also toxic if ingested in high doses.
A method is also known for producing Brewer's yeast having an intracellular chromium concentration of about 200 ppm by cultivating the yeast in a broth where the source of trivalent chromium is from a mixture of chromium oxide and certain amino acids. [Szalay, U.S. Pat. No. 4,343,905]. Although 80% of the chromium produced by this method is reported to be GTF chromium, this method is hard to reproduce due to the insolubility of the chromium oxide. In other words, the insolubility of chromium oxide results in a low yield of GTF chromium produced by this method. To the extent that this method also involves internalization of chromium oxide without its metabolization, it results in inorganic chromium oxide that is merely mixed with the yeast structural material. Since chromium oxide is known to be significantly toxic to the human system, this method is not preferred as a method for making a dietary supplement.
There remains a need in the art for concentrated forms of GTF chromium--complexes bearing the structure and activity found in naturally occurring Brewer's yeast, but having a higher biological activity, and which may be used in high concentrations because of their low toxicity. In addition, there is a need in the art for methods to produce such complexes.